After a time, if you add too much butter, the sauce will curdle and turn oily, as described by Francatelli.
Of course, in everyday life it is not necessary to have the butter sauce so rich, still it is simply ridiculous to thicken a pint of milk, or a pint of water, with a little butter and flour, and then call it butter sauce or melted butter.

Suppose we have a large white cabbage, like those met with in the West of England, and we are going to make a meal off it in conjunction with plenty of bread.

Suppose the cabbage is sufficiently large for six persons, surely half a pound of butter is not an excessive quantity to use in making butter sauce for the purpose.

Yet prejudice is such that if we use half a pound of butter for the butter sauce, housekeepers consider it extravagant.

On the other hand, if the butter were placed on the table, and the six persons helped themselves, and ate bread and butter with the cabbage and finished the half-pound, it would not be considered extravagant.